Flexibilizer additive

Butyl latex can be used in packaging and as a tackifying and flexibilizing additive in higher strength adhesives for adhesion of polyethylene and polypropylene. 

Since many of the difunctional epoxy diluents are added to epoxy adhesive formulations as flexibilizers as well as viscosity reducers, they are discussed in greater detail in Chap. 8 with other flexibilizing additives. 

C. End-Uses Flexibilizing additive strapping tape fabric coatings and paper coating. 

The percentage of solids in the dispersion adhesives is 35-55%, in some cases as much as 70%, the rest is water, which after the adhesive application must either be completely evaporated (ventilation time) or diffuse into the joined parts (wood, textiles, concrete, foams, leather). The film formation temperature in types containing plasticizers and flexibilizing additives is lower than in types that are free of plasticizers. Additives, so-called high boilers (ethyl glycol, ethyl glycol acetate, ethylhexanol), are used to bring the film formation temperature down. 

Thermoplastic perfluorocyclobutane arylene ether polymers offer a solvent soluble, melt processable, low dielectric alternative to conventional fluoropolymers. Relatively little time has been spent on their development, however. The bifimctional monomers have proven quite useful as comonomers in modifying the thermal and mechanical properties of high Tg thermoset copolymers. In particular, the siloxane PFCB polymer discussed earlier (Figure 3) exhibits a Tg = 16 C (DSC) thereby providing a reactive toughening or flexibilizing additive either as block type copolymers or comonomer for random incorporation (8),... 

BP. These nitrile alloy membranes are compounded from PVC, flexibilized by the addition of butadiene—acrylonitrile copolymers, PVC, and other proprietary ingredients. Typically reinforced with polyester scrim, NBP membranes are 1 mm thick and have a width of 1.5 m. They ate ptedominandy used in mechanically fastened roofing systems. NBP membranes exhibit excellent teat and puncture resistance as well as good weatherabihty, and remain flexible at low temperatures. They ate resistant to most chemicals but ate sensitive to aromatic hydrocarbons. The sheet is usually offered in light colors. The physical characteristics of NBP membranes have been described (15). 

Flexibilized epoxy resins are important structural adhesives [69]. Liquid functionally terminated nitrile rubbers are excellent flexibilizing agents for epoxy resins. This liquid nitrile rubber can be reacted into the epoxy matrix if it contains carboxylated terminated functionalities or by adding an amine terminated rubber. The main effects produced by addition of liquid nitrile rubber in epoxy formulations is the increase in T-peel strength and in low-temperature lap shear strength, without reducing the elevated temperature lap shear. 

The addition of a single monochromating crystal gives the device great flexibil ity, since one has independent control over the collimation, by the number of reflections, and the bandpass, controlled by the width of the reflection of the monochromating crystal. Figure 2.16 shows one variant, a three-reflection... 

PVC is flexibilized by addition of plasticizers as already noted. It is also made more flexible through blending with elastomers that act as impact modifiers. These blends are used when impact resistance is essential. 

Intractable polymers, such as polyvinyl chloride (PVC), may be flexibilized, to some extent, by the formation of copolymers, such as the copolymers of vinyl chloride and vinyl acetate or octyl acrylate, or by the addition of nonvolatile low-molecular-weight compounds (plasticizers) having solubility parameters similar to those of the polymer. Thus PVC is plasticized by the addition of dioctyl phthalate. The flexibility of these products is proportional to the amount of plasticizer added. Copolymers, such as the vinyl chloride-vinyl acetate copolymer, require less plasticizer to obtain the same degree of flexibility. 

Anhydrides generally provide pot lives of days or months and cure usually at 100-180°C with very little exotherm. Tertiary amines accelerate the time for gelation but still require the elevated temperature cure to obtain optimum properties. Anhydrides usually give brittle products but the addition of polyether flexibilizing groups yields more elastomeric products [44]. 

Some dicyanate-containing compositions, which contain rubbers as flexibilizing components, were described in the preceding chapters. There were also patent applications made, where dicyanates were claimed as additives in typical rubber mixtures. In such mixtures, butadiene-acrylonitrile rubber is used. The main components of such binders are nitrile rubber, BPA/DC and methylethylketone. They contain, moreover, Zn octoate and Fe203 [144] or ZnO and sulfur [145]. Isoprene-acryloni-trile rubber, BPA/DC prepolymer, Zn octoate, DABCO and benzoyl peroxide were dissolved in a methylethylketone-dimethylformamide mixture. Glass fiber was impregnated with the obtained solution [146]. 

Another common method of flexibilizing epoxy adhesives is by blending the primary epoxy resin with other, more elastic polymers. Epoxy-nylon, epoxy-polysulfide, and to a certain extent epoxy-urethane hybrids use such a mechanism to provide flexibility. These flexibilizers are important additives for epoxy adhesives even though they may reduce certain... 

The morphology of these systems with the additional piperidine indicates that more of the particles become less distinct in the matrix. The particle boundaries are less well defined, and the fracture surface of the particles becomes similar to the matrix—i.e., the striations in the matrix will carry over within the particle boundaries. We believe that the additional piperidine enhances linear copolymerization to give the characteristics of flexibilization to the resin. This brings the modulus of... 

By 1950 two theories had evolved to account for the major "flexibilizing" effect of plasticization the "lubricity" theory and the "gel" theory ( ). In addition, the "free volume" theory devised to explain fluid flow was also being adapted to plasticization (10). 

Early researchers who worked on flexible vinyl formulations were convinced that the technique of external plasticizing was doomed because of inadequate "permanence" in the composition. Although good initial properties were attainable, it was felt these could not be maintained. Consequently, a great amount of study was devoted to flexibilizing by "internal plasticization" through copolyraerization. Resins so developed, however, are usually found unable to meet the wide range of property demands and therefore in turn require additional external plasticization. 

In PVC/nitrile rubber blends, PVC is added more as an ozone resistant additive. In these ther-moplastically processable blends, PVC is flexibil-ized enough to be used for soft goods, wire jacketing, hoses, gaskets and seals. When the NBR contains >25% acrylonitrile, it becomes miscible with PVC and at < 20% acrylonitrile level, it is fairly compatible due to partial miscibility [Matso et al., 1969]. 

In addition to chlorinated polyethylene, three other major types of modifiers are blended commercially with PVC in order to flexibilize the composition. Usually 30-60% modifier levels are employed. These flexibilizing modifiers usually have some degree of miscibility with PVC. A list of the commercial flexibilizing modifiers and their advantages are shown in Table 15.10. 

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